The goal of this project is to understand how odors are represented by populations of olfactory receptor neurons at the level of their input to the olfactory bulb, and to analyze how these representations are modified at the synapse between olfactory receptor neurons and o1factory bulb neurons. While responses of single olfactory receptor neurons to odors have been well characterized, the strategy by which odor information is encoded across the entire population of neurons is poorly understood. A critical step in this process is the convergence of receptor neurons onto glomeruli of the olfactory bulb, where a spatial map of odor sensitivity is generated and the synaptic processing of olfactory information begins. This study will focus on the coding and processing of information about odors at this first, critical level of the olfactory pathway by selectively imaging activity in olfactory receptor neuron terminals. In particular, this study will focus on how different odorants, and different concentrations of the same odorant, are represented in terms of spatial patterns of input to olfactory bulb glomeruli. This study will also characterize a newly-established neuronal pathway for presynaptic inhibition of olfactory receptor neuron input to the olfactory bulb, the functional significance of which has yet to be explored. Specifically, this study will: 1) investigate how odors are represented by receptor neuron input to the olfactory bulb, 2) functionally characterize pathways mediating presynaptic inhibition of receptor neuron input to the olfactory bulb, and 3) investigate the role of this presynaptic inhibition in shaping the representation of odors. Together, these experiments will constitute a significant step towards understanding how odor quality is encoded at a specific level of the olfactory pathway. Understanding the basic functions of the olfactory system can potentially lead to improved diagnosis and treatment of diseases of the nervous system.